This invention relates to treating indoor air by passing the air over and through the foliage and roots of hydroponically-nourished plants.
Airborne contaminants can build up in a room where ventilation is not adequate, giving air its stale quality. The contaminants can include organic detritus from human and other living occupants of the room, and can include organic and non-organic vapours, gases, and particles, such as benzine, soot, dust.
The volatile organic contaminants (VOCS) can be broken down by microbial action. But one problem is that the contaminants are present in such small concentrations that colonies of microbes would not be viable, if the microbes were to feed exclusively or mainly on the tiny traces of organic materials that make up the contaminants.
The technique has arisen of providing plants, to assist in removing organic airborne contaminants. The plants are provided especially in respect of those rooms of a building in which the inevitable imperfections and variables of the building""s air ventilation and filtration system has meant that that particular room is not achieving, as a matter of fact, the number of air changes in a given period of time, as needed to keep the air fresh. These rooms or pockets of stale air, where they occur, might be relieved by opening the windows, but many modem buildings do not have openable windows.
The publication of research indicating that plants improve air quality makes the use of indoor plants in buildings appealing, and widespread. And of course, plants may be placed in a room just for the aesthetic benefits. However, the fact is that simply adding a few pot-plants into a room does not, as a rule, do much to improve air quality.
The microbe colonies that can feed on, and thereby break down, airborne organic pollutants, tend to become established primarily on the roots of plants. The micro-biological reactions that lead to the breakdown of the airborne organic pollutants arise from microbe colonies that are aerobic, i.e that derive oxygen mainly from the atmosphere. The amount of exposure to air that such colonies need, in order to become viable, is quite small; thus, plant roots need only a minimum of aeration in order for the colonies to be viable.
Laboratory tests have shown that microbial reactions arising from plants, and especially arising from the aerobic microbes that become established in the roots of plants, can improve the rate of breakdown of many airborne organic contaminants. However, as mentioned, it is one thing for laboratory tests to show that microbe colonies on plant roots can break down airborne organic pollutantsxe2x80x94and quite another to actually make a difference to the quality of air in the room. That plants can improve indoor air quality is known; the present invention is concerned with actually achieving a worthwhile improvement in the air quality in a stale-air room, by the use of a practical and economical apparatus.
The present invention is aimed at arranging plants, and in passing air through plants, in such manner as to enhance the ability of microbe colonies associated with the plants to break down airborne pollutants. The invention is intended mainly for use in cases where the ventilation system of a building has left a room or other pocket in the building with an inadequate or reduced ventilation throughtlow, to the extent that the air in that room or pocket is characterised as stale.
Architects are aware of the complaints of occupants of stale-air rooms, and tend to over-engineer the ventilation system, by large margins (which can be expensive) in the hope of avoiding such complaints. With the present invention, stale air pockets can be alleviated, and the aim is that the architect, knowing this, may more economically engineer the ventilation system with smaller margins.
The futility is known, of trying to freshen up the air in a room by simply placing a few (or many) pot-plants in the room. Prior approaches have included the much more controlled and structured environment of hydroponic cultivation techniques. However, while it is known that the air should be passed over the roots of the plants, for best results, still designers have had difficulty in engineering a mechanical arrangement whereby large volumes of air can be passed over and through the root zones. In some prior proposals, the matrix panel in which the plants are physically mounted has been horizontal, and it has proved difficult to arrange for adequately large volumetric flow-rates of air to pass through the roots of the plants, given that the roots are kept under water.
In other proposals, the plants have not been nourished hydroponically, but have been planted in ordinary organic soil, and watered occasionally. The difficulty here is that the nutrients in the soil only last for a limited period, and also that salts and waste products build up in the root zone of the soil.
It is known to take dust and particulate pollutants out of air by means which do not involve plants, for example by means of a wet scrubber. This amounts to passing the air through a (falling) curtain of water. The particles are sorbed out of the air, into the water droplets; that is to say, the drops of water in the curtain develop an electrostatic potential that attracts the particulates, causing them to remain with the water. However, in this (plant-less) system, the contaminants remain intact, and build up concentration in the scrubber apparatus, where they might cause even more problems than when diluted in the air.
The present invention is aimed at providing an air cleansing system which can treat a large volumetric flow rate of air. The large volumetric throughput means that air in the room can be circulated over and through the roots, again and again, many times. Again it is noted that the pollutants are present in the air only in very tiny traces. It is the fact of the prolonged exposure of the occupants of the room to the pollutants, not high concentrations of the pollutants, that makes the pollutants harmful. It is recognised that the way to remove such tiny traces from the air is to pass the air through the treatment system many times, which is why the large flow-rates are necessary.
The invention aims to provide an air-cleansing system in which large airflows can be effectively treated, and to do so by means of an apparatus that operates consistently and efficiently over a long period of time (e.g years), basically with very little attention. Since the system is mainly intended to be housed in an already-existing room, in a building, the invention aims also to provide an apparatus which can be made light in weight, and self-contained and self-supporting enough to be easy to install. Also, the invention aims to provide a system in which the apparatus can be manufactured in-factory, and can be factory-prepared for installation, whereby the apparatus can be shipped, and installed, and brought into operation, with a minimum of skilled knowledge and attentive care on the part of the installer and other operatives.
In order to break down the airborne contaminants, it is recognised that the air has to be circulated and recirculated through the plant roots, very many times. It can be many hours, or days, before an improvement (i.e a significant reduction in the concentrations of the contaminants) can be detected and noticed. One key to the successful performance of an air freshening treatment apparatus is that the apparatus should be able to handle large volumetric flow rates of air, and should be able to direct and focus the air onto the plant roots, where the microbe colonies are established.
An air-cleansing unit that embodies the present invention includes a plant-box, and the plant-box has a front wall, and enclosing walls, which enclose and define a plenum chamber. The plenum has an air outlet port, in one of the walls. The unit includes a powered fan, which is so disposed in the apparatus as to be effective to receive air from the plenum, through the air outlet port, and to discharge the air.
Preferably, the front wall of the plant-box includes a root matrix panel, which is made from air-permeable material, and is so arranged in the apparatus as to allow air to pass therethrough, into the plenum. The material of the panel is structurally solid, and is of such porosity or fibrosity as to enable the roots of plants to infiltrate into the material, and to provide physical and mechanical anchorage and support for the roots and foliage of the plants.
Preferably, the plants are grown and nourished hydroponically. The material of the root matrix panel of the plant-box is inert with respect to microbiological actions and reactions associated with the mass of plants. The apparatus includes a hydroponic water and nutrient circulation system. A water outlet is positioned above the root matrix panel, and is so arranged that hydroponic water passes out from the outlet, down onto the root matrix panel.
Preferably, the hydroponic water trickles down, from the outlet, over and through the material of the root matrix panel, and over and through the roots of the plants embedded therein. The system is so arranged that the roots of the mass of plants are kept substantially constantly wetted by the hydroponic water.
Preferably, the root matrix panel is disposed nearly vertically, but preferably with a slight incline to the vertical. Hydroponic water flows downwards, under gravity, over and through the material of the panel, and over and through he roots of the plants embedded therein, while air passes through the panel, into the plenum, in a direction that is at least roughly horizontal.
Arranged thus, the apparatus can treat large through-flows of air, over long periods. The VOCs and organic dust particles are efficiently sorbed out of the air, onto the water, becoming deposited onto the roots of the plants, where the microbes are present in viable colonies. The colonies are nourished by the normal plant actions; the colonies consume and break down the pollutants as a side effect. It may be noted that green foliage can also be effective to reduce the concentration of carbon monoxide in air, provided the air is kept moving over the foliage, which is indeed what happens in the apparatus as described.
To run efficiently over a long period, the apparatus should be built in, and automated as required. Thus, the apparatus should be provided with mains electricity, a water supply, a water drain, and nutrient reservoirs. If the light in the room is low, extra bright lights should also be provided, to enhance the hydroponic viability of the plants.
The physical movement of the water, in constantly trickling through the matrix panel, helps to ensure that the water maintains the electrostatic polar potential that sorbs the VOCs, dust, etc, out of the passing air.